Reverse Engineering for Beginners

CHAPTER 21. STRUCTURES CHAPTER 21. STRUCTURES

Listing 21.10: Optimizing Xcode 4.6.3 (LLVM) (Thumb-2 mode)

var_38 = -0x38

var_34 = -0x34

PUSH {R7,LR}

MOV R7, SP

SUB SP, SP, #0x30

MOVS R0, #0 ; time_t *

BLX _time

ADD R1, SP, #0x38+var_34 ; struct tm *

STR R0, [SP,#0x38+var_38]

MOV R0, SP ; time_t *

BLX _localtime_r

LDR R1, [SP,#0x38+var_34.tm_year]

MOV R0, 0xF44 ; "Year: %d\n"

ADD R0, PC ; char *

ADDW R1, R1, #0x76C

BLX _printf

LDR R1, [SP,#0x38+var_34.tm_mon]

MOV R0, 0xF3A ; "Month: %d\n"

ADD R0, PC ; char *

BLX _printf

LDR R1, [SP,#0x38+var_34.tm_mday]

MOV R0, 0xF35 ; "Day: %d\n"

ADD R0, PC ; char *

BLX _printf

LDR R1, [SP,#0x38+var_34.tm_hour]

MOV R0, 0xF2E ; "Hour: %d\n"

ADD R0, PC ; char *

BLX _printf

LDR R1, [SP,#0x38+var_34.tm_min]

MOV R0, 0xF28 ; "Minutes: %d\n"

ADD R0, PC ; char *

BLX _printf

LDR R1, [SP,#0x38+var_34]

MOV R0, 0xF25 ; "Seconds: %d\n"

ADD R0, PC ; char *

BLX _printf

ADD SP, SP, #0x30

POP {R7,PC}

00000000 tm struc ; (sizeof=0x2C, standard type)

00000000 tm_sec DCD?

00000004 tm_min DCD?

00000008 tm_hour DCD?

0000000C tm_mday DCD?

00000010 tm_mon DCD?

00000014 tm_year DCD?

00000018 tm_wday DCD?

0000001C tm_yday DCD?

00000020 tm_isdst DCD?

00000024 tm_gmtoff DCD?

00000028 tm_zone DCD? ; offset

0000002C tm ends

21.3.3 MIPS.

Listing 21.11: Optimizing GCC 4.4.5 (IDA)

1 main:
2
3 ; IDA is not aware of structure field names, we named them manually:
4
5 var_40 = -0x40
6 var_38 = -0x38
7 seconds = -0x34